Raspberry Pi + GPIOzero: press button to change a variable in a loop (while the loop keeps on running)

I'm trying to make a visual metronome of sorts in which I press a button in order to change the bpm. Once the bpm is 85, if the button is pressed once more, if goes back to the default bpm (of 120). t this is my code:

from gpiozero import *
from time import sleep

bpmButton = Button(6)
bpmLED = LED(14)

#This function defines the flashing light
def lightFlash(luz, tiempoOn, rate):
    luz.on()
    sleep(tiempoOn)
    luz.off()
    sleep(rate-tiempoOn)

#This changes the flashing light according to the bpm
def bpmIndicator(bpm):
    durFlash = 60 / bpm
    durLuz = 0.2
    lightFlash(bpmLED, durLuz, durFlash)
    
#Initial bpm
currentBpm = 120


while True: 
    
    if bpmButton.is_pressed:
        currentBpm -= 5 
    if currentBpm < 80:
        currentBpm= 120
print(currentBpm)
bpmIndicator(currentBpm)

And this works. However, when I try putting whats in the "while" loop in a function it doesn't work anymore. I don't seem to be able to store the new currentBpm value. Here's my attempt at trying to convert it into a function.

def bpmChanger(bpm):
    if bpmButton.is_pressed:
        bpm -= 5    
        if bpm < 80:
            bpm= 120
    print(bpm)
    return(bpm)
    
currentBpm = 120


while True: 
    
    bpmIndicator(bpmChanger(currentBpm))

I'd like to save whatever value bpmChanger returns, as I plan on using it later on in the project.

As mentioned you have to tell python, that you want to use the "bpmButton" variable from outside the function. Because otherwise python instantiates a new variable with the same name, but no value. Try this:

def bpmChanger(bpm):
  global bpmButton  # EDIT
  if bpmButton.is_pressed:
     bpm -= 5    
  if bpm < 80:
     bpm= 120
  print(bpm)

  return(bpm)